In-situ characterisation of catalysts has become increasingly important. It is however not easy to measure or monitor physical or chemical changes in a working catalyst. The reasons for this are that the catalyst is inside a reactor and therefore not visible and neither can it be removed or sampled without interfering with the reaction. It is therefore necessary to find some property of the catalyst that can be measured without disturbing or interfering with the reaction. This property also needs to be able to provide the necessary information about the catalyst. The magnetic properties of the sample of interest fulfil these requirements since they can be measured without direct interaction with the sample and from them the necessary information about the sample can be deduced.
By performing a hysteresis measurement comprising measurement of magnetisation as function of an external magnetic field of the catalysts which contains ferro-magnetic material inside the reactor, magnetic saturation, magnetic remnance and coercive field can be measured. These properties allow the calculation of other useful properties of the catalyst such as the amount of metal phase present (that is the degree of reduction) as well as sintering or crystallite break-up of ferro-magnetic and super-paramagnetic material. These measurements could also be used to determine crystallite sizes and crystallite size distributions of the magnetic matter in a sample.
Vibrating sample magnetometers are commercially available devices for characterisation of magnetic material. In these, a sample is secured in a holder which is either oscillated within a magnetic field and associated signal pickup coils or the magnetic field or signal pickup coils oscillated with respect to it. Quartz is often used for the sample holder as it is non-magnetic and thus does not affect the magnetic field or the disturbances created by the sample moving therein.
Experimental devices have also been proposed which include a tubular quartz reactor in which a sample is secured. These magnetometers usually offer the possibility to record magnetic properties of such material at different temperatures. However no measurements at controlled environments and elevated pressure are possible on these devices. In this context, elevated pressures are those above about 5 bar.
No devices are available which have the capability of characterising ferro- and super-paramagnetic material (including catalysts) at controlled gas environment at flow conditions at elevated pressures, that is at industrially fully relevant conditions in, for example, catalytic applications. Under such conditions, however, the characterisation of the magnetic catalyst behaviour can give important information on effects of catalyst oxidation and or reduction and or effects of catalyst sintering. This information helps to understand effects of catalyst deactivation and is of crucial importance for the development of improved catalysts.